Invalid Memo.decrypt() type annotation

[Algruun]

Method decrypt in bithsares/memo.py has invalid type annotation.

    def decrypt(self, memo):
        """ Decrypt a memo

            :param str memo: encrypted memo message
            :returns: encrypted memo
            :rtype: str
        """

Here it says that memo should be str, but it used like a dict

return BtsMemo.decode_memo(
            PrivateKey(memo_wif),
            PublicKey(
                self.from_account["options"]["memo_key"],
                prefix=self.bitshares.rpc.chain_params["prefix"]
            ),
            memo.get("nonce"),
            memo.get("message")
        )